@slevin, the case fan is 120x120x25mm. Here are the replacement fans that have served me very well (and keep the system from sounding like a jet engine):
Replacement Fans –
- Case Fan – Noctua NF-P12 Redux-1300 120x120x25mm 1300RPM, 3-Pin Fan
- CPU Fan – Gelid Solutions Silent 7 Series 70x70x15mm 3-Pin Fan
- PSU Fans – TWO Sunon 40x40x20mm 12V DC VAPO 5.5CFM, 2-Wire Fans (HA40201V4-1000U-A99)
- 20mm is shorter than the length of the original PSU fans so may want to cover gap with tape or other material to maintain original airflow pattern